Crystal structure of 3,14-dimethyl-2,13-diaza-6,17-diazoniatricyclo[16.4.0.07,12]docosane bis(perchlorate) from synchrotron X-ray data

In the title salt, C20H42N4 2+·2ClO4 −, the macrocyclic dication lies about an inversion center. In the crystal, the organic dication and perchlorate anions are linked through N—H⋯O, C—H⋯O and N—H⋯N hydrogen bonds, forming a three-dimensional network.


Chemical context
The macrocyclic compound, 3,14-dimethyl-2, 6,13,17-tetraazatricyclo(16.4.0.0 7,12 )docosane (C 20 H 40 N 4 ) contains a cyclam backbone with two cyclohexane subunits and two methyl groups are also attached to carbon atoms 3 and 14 of the propyl chains that bridge opposite pairs of N atoms in the structure. The macrocycle is basic and readily captures two or four protons to form the [C 20 H 42 N 4 ] 2+ dication or the [C 20 H 44 N 4 ] 4+ tetracation in which all of the N-H bonds are generally available for hydrogen-bond formation (Moon et al., 2021).
We report here the preparation of a new dicationic compound, [C 20 H 42 N 4 ](ClO 4 ) 2 , (I) and its structural characterization by synchrotron single-crystal X-ray diffraction.

Structural commentary
An ellipsoid plot of the molecular components in (I) with the atom-numbering scheme is shown in Fig. 1. The asymmetric unit consists of one half of the macrocyclic dication, which lies about a center of inversion, and one perchlorate anion. The four N atoms are coplanar, and the two methyl substituents are anti with respect to the macrocyclic plane as a result of the molecular inversion symmetry. The [C 20 H 42 N 4 ] 2+ dication adopts an endodentate conformation and trans-III configuration along the center of the macrocyclic cavity. The endo conformation of the dication may be due to the intramolecular N-HÁ Á ÁN hydrogen-bonding interaction. Within the centrosymmetric diprotonated amine unit, the C-C and N-C bond lengths range from 1.5173 (18) to 1.5368 (18) Å and from 1.4795 (16) to 1.5044 (16) Å , respectively. The range of N-C-C and C-N-C angles is 108.89 (11) to 113.50 (11) and 113.46 (11) to 114.61 (11) , respectively. The bond lengths and angles within the dication are comparable to those found in the free ligand or other cations in (C 20 H 40 N 4 )Á2C 11 H 10 O (Choi et al., 2012c), [C 20 H 42 N 4 ](SO 4 )Á2MeOH (White et al., 2015) and [C 20 H 42 N 4 ][Fe{HB(pz) 3 }(CN) 3 ] 2 Á2H 2 OÁ2MeOH (Kim et al., 2004;pz = pyrazolyl). The protonation of the N atoms may depend on the location of the neighboring counter-anions involved in hydrogen bonding. The bond-length difference can be noticed for several N-C bonds. The N-C bond length involving the non-protonated N1 atom is shorter than that involving protonated N2 atom, e.g. N1-C2 [1.4817 (18)  . Each of the two hydrogen atoms of N2 and N2 0 (Àx + 1, Ày + 2, Àz + 1) is involved in hydrogen bonding with both of the two remaining nitrogen atoms (Table 1). The intramolecular hydrogen bonding plays a substantial role in maintaining the endodentate geometry of the diprotonated macrocyclic cation. The Cl-O bond distances in the tetrahedral ClO 4 À anion vary from 1.4218 (19) to 1.4529 (16) Å , and the O-Cl-O angles vary from 106.45 (10) to 110.51 (12) . The distorted geometry of the ClO 4 À anion undoubtedly results from its involvement in hydrogen-bonding interactions with the organic cation.
acceptors. The ClO 4 À anions are connected to the [C 20 H 42 N 4 ] 2+ dication by N-HÁ Á ÁO hydrogen bonds. The macrocyclic dication is linked to a neighboring ClO 4 À anion through a very weak C-HÁ Á ÁO hydrogen bond. The extensive array of these contacts generates a three-dimensional network structure (Fig. 2), and these hydrogen-bonding interactions help to stabilize the crystal structure.

Synthesis and crystallization
Commercially available trans-1,2-cyclohexanediamine and methyl vinyl ketone (Sigma-Aldrich) were used as provided. All chemicals were reagent grade and used without further purification. As a starting material, macrocycle 3,14-dimethyl-2,6,13,17-tetraazatricyclo(16.4.0.0 7,12 )docosane, L, was prepared according to a published procedure (Kang et al., 1991). Macrocycle L (0.034 g, 0.1 mmol) was suspended in methanol (20 mL) and the pH was adjusted to 3.0 with 0.5 M HClO 4 . The mixture was stirred magnetically for 30 min and the resulting solution was filtered. The neat filtrate was allowed to stand for one week to give block-like colorless crystals of (I) suitable for X-ray structural analysis.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 2. All non-hydrogen atoms were refined anisotropically. All C-bound H atoms and the hydrogen atoms of the diprotonated amine (H2A and H2B) were placed in geometrically idealized positions and constrained to ride on their parent atoms, with C-H distances of 0.97-0.98 Å and an N-H distance of 0.99 Å , and with U iso (H) values of 1.5 and 1.2 times, respectively, that of the parent atoms. The one N-bound H atom (H1N1) of the amine was assigned based on a difference-Fourier map, and a U iso (H) value of 1.5U eq (N1).  Data collection: PAL BL2D-SMDC (Shin et al., 2016); cell refinement: HKL3000sm (Otwinowski & Minor, 1997); data reduction: HKL3000sm (Otwinowski & Minor, 1997); program(s) used to solve structure: SHELXT2018 (Sheldrick, 2015a); program(s) used to refine structure: SHELXL2018 (Sheldrick, 2015b); molecular graphics: DIAMOND 4 (Putz & Brandenburg, 2014); software used to prepare material for publication: publCIF (Westrip, 2010). Special details Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes.